A semiconductor device has been encapsulated for the purpose of protecting a semiconductor element, ensuring electric insulation and achieving easy handling property, and the transfer molding has been a mainstream with the use of an epoxy resin composition from the viewpoints of the productivity, cost, reliability and the like. In response to the market requirements of decreasing size, decreasing weight and increasing performance of electronic devices, a novel joint technology such as surface mounting has been developed and commercialized, in addition to high integration of semiconductor elements, and miniaturization and high density of semiconductor devices. This technical trend has also influenced on a resin composition for encapsulating a semiconductor, and required performance has been upgraded and diversified year by year.
For example, as for solders used for surface mounting, use of lead-free solder instead has been promoted against the background of environmental problems. The melting point of lead-free solders is higher than that of the conventional lead/tin solders, and the reflow mounting temperature is increased from conventional 220 to 240 degrees centigrade, to 240 to 260 degrees centigrade, so that resin cracks are easily formed, delamination easily occurs inside the semiconductor device, or solder resistance is not sufficient in the conventional encapsulating resin composition in some cases.
Furthermore, for the purpose of imparting flame retardance, a bromine-containing epoxy resin and an antimony oxide have been used as a flame retardant in the conventional encapsulating resin composition. However, there is a growing opportunity to eliminate such compounds from the viewpoints of recent environmental protection and improvement of safety.
Furthermore, in recent years, electronic devices such as cars and mobile phones which are intended for outdoor use have come into wide use. In these applications, the operational reliability under severer environment than the conventional personal computers or household electric appliances has been in demand. In particular, high-temperature storage characteristics have been demanded as one of mandatory requirements in automotive applications, so that it is necessary to maintain the operating and functioning of a semiconductor device at a high temperature of 150 to 180 degrees centigrade.
As a conventional technology, there have been proposed a method of enhancing high-temperature storage characteristics and solder resistance by combining an epoxy resin having a naphthalene skeleton and a phenol resin curing agent having a naphthalene skeleton (Patent Documents 1 and 2) and a method of enhancing high-temperature storage characteristics and flame resistance by combining a phosphorus containing compound (Patent Documents 3 and 4). However, it is hard to mention that a sufficient balance among flame resistance, continuous molding property and solder resistance has been achieved through these methods in some cases. As described above, with miniaturization and popularization of automotive electronic devices, there has been demanded an encapsulating resin composition which is well balanced among flame resistance, solder resistance, high-temperature storage characteristics and continuous molding property.